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+/* libstdbuf -- a shared lib to preload to setup stdio buffering for a command
+ Copyright (C) 2009-2022 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <https://www.gnu.org/licenses/>. */
+
+/* Written by Pádraig Brady. LD_PRELOAD idea from Brian Dessent. */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdint.h>
+#include "system.h"
+
+/* Deactivate config.h's "rpl_"-prefixed definitions, since we don't
+ link gnulib here, and the replacements aren't needed. */
+#undef fprintf
+#undef free
+#undef malloc
+#undef strtoumax
+
+/* Note currently for glibc (2.3.5) the following call does not change
+ the buffer size, and more problematically does not give any indication
+ that the new size request was ignored:
+
+ setvbuf (stdout, NULL, _IOFBF, 8192);
+
+ The ISO C99 standard section 7.19.5.6 on the setvbuf function says:
+
+ ... If buf is not a null pointer, the array it points to _may_ be used
+ instead of a buffer allocated by the setvbuf function and the argument
+ size specifies the size of the array; otherwise, size _may_ determine
+ the size of a buffer allocated by the setvbuf function. ...
+
+ Obviously some interpret the above to mean setvbuf(....,size)
+ is only a hint from the application which I don't agree with.
+
+ FreeBSD's libc seems more sensible in this regard. From the man page:
+
+ The size argument may be given as zero to obtain deferred optimal-size
+ buffer allocation as usual. If it is not zero, then except for
+ unbuffered files, the buf argument should point to a buffer at least size
+ bytes long; this buffer will be used instead of the current buffer. (If
+ the size argument is not zero but buf is NULL, a buffer of the given size
+ will be allocated immediately, and released on close. This is an extension
+ to ANSI C; portable code should use a size of 0 with any NULL buffer.)
+ --------------------
+ Another issue is that on glibc-2.7 the following doesn't buffer
+ the first write if it's greater than 1 byte.
+
+ setvbuf(stdout,buf,_IOFBF,127);
+
+ Now the POSIX standard says that "allocating a buffer of size bytes does
+ not necessarily imply that all of size bytes are used for the buffer area".
+ However I think it's just a buggy implementation due to the various
+ inconsistencies with write sizes and subsequent writes. */
+
+static char const *
+fileno_to_name (const int fd)
+{
+ char const *ret = NULL;
+
+ switch (fd)
+ {
+ case 0:
+ ret = "stdin";
+ break;
+ case 1:
+ ret = "stdout";
+ break;
+ case 2:
+ ret = "stderr";
+ break;
+ default:
+ ret = "unknown";
+ break;
+ }
+
+ return ret;
+}
+
+static void
+apply_mode (FILE *stream, char const *mode)
+{
+ char *buf = NULL;
+ int setvbuf_mode;
+ uintmax_t size = 0;
+
+ if (*mode == '0')
+ setvbuf_mode = _IONBF;
+ else if (*mode == 'L')
+ setvbuf_mode = _IOLBF; /* FIXME: should we allow 1ML */
+ else
+ {
+ setvbuf_mode = _IOFBF;
+ char *mode_end;
+ size = strtoumax (mode, &mode_end, 10);
+ if (size == 0 || *mode_end)
+ {
+ fprintf (stderr, _("invalid buffering mode %s for %s\n"),
+ mode, fileno_to_name (fileno (stream)));
+ return;
+ }
+
+ buf = size <= SIZE_MAX ? malloc (size) : NULL;
+ if (!buf)
+ {
+ /* We could defer the allocation to libc, however since
+ glibc currently ignores the combination of NULL buffer
+ with non zero size, we'll fail here. */
+ fprintf (stderr,
+ _("failed to allocate a %" PRIuMAX
+ " byte stdio buffer\n"),
+ size);
+ return;
+ }
+ /* buf will be freed by fclose. */
+ }
+
+ if (setvbuf (stream, buf, setvbuf_mode, size) != 0)
+ {
+ fprintf (stderr, _("could not set buffering of %s to mode %s\n"),
+ fileno_to_name (fileno (stream)), mode);
+ free (buf);
+ }
+}
+
+/* Use __attribute to avoid elision of __attribute__ on SUNPRO_C etc. */
+static void __attribute ((constructor))
+stdbuf (void)
+{
+ char *e_mode = getenv ("_STDBUF_E");
+ char *i_mode = getenv ("_STDBUF_I");
+ char *o_mode = getenv ("_STDBUF_O");
+ if (e_mode) /* Do first so can write errors to stderr */
+ apply_mode (stderr, e_mode);
+ if (i_mode)
+ apply_mode (stdin, i_mode);
+ if (o_mode)
+ apply_mode (stdout, o_mode);
+}